Base station and control method thereof

ABSTRACT

A macro base station MeNB in a mobile communication system that supports a carrier aggregation technology defined in a 3GPP standard, communicates with a pico base station PeNB #1 via an X2 interface. The macro base station MeNB transmits information to the pico base station PeNB the information being used when the pico base station PeNB determines a component carrier requested to be limitedly used by the macro base station MeNB or a component carrier requested to be released from use limitation by the macro base station MeNB.

TECHNICAL FIELD

The present invention relates to a base station in a mobilecommunication system that supports a carrier aggregation technology anda control method thereof.

BACKGROUND ART

As the next-generation mobile communication system for achieving highspeed communication with high capacity, standardization of LTE Advancedobtained by sophisticating LTE (Long Term Evolution) has been inprogress in 3GPP (3rd Generation Partnership Project) that is astandardization group.

In order to achieve to widen a band while ensuring backwardcompatibility with LTE, LTE Advanced introduces a carrier aggregationtechnology in which a carrier (a frequency band) of LTE is positioned asa component carrier, and a plurality of component carriers arecollectively used to perform radio communication (for example, see NonPatent Literature 1).

CITATION LIST Non Patent Literature

-   Non Patent Literature 1: 3GPP Technical Specification TS 36.300    V10.3.0, “5.5 Carrier Aggregation”

SUMMARY OF THE INVENTION

Meanwhile, in LTE Advanced, it is widely discussed to reduceinterference in the aforementioned carrier aggregation technology.

Therefore, an object of the present invention is to solve theaforementioned problems in a mobile communication system that supports acarrier aggregation technology defined in 3GPP standard.

To solve the aforementioned problem, the present invention has followingfeatures.

The feature of a base station according to the present invention issummarized as follows. Abase station (for example, a macro base stationMeNB) in a mobile communication system that supports a carrieraggregation technology defined in a 3GPP standard, transmits informationto another base station (for example, a pico base station PeNB #1) on anX2 interface or an S1 interface, the information being used when theother base station determines a component carrier requested to belimitedly used by the base station or a component carrier requested tobe released from use limitation by the base station.

The feature of a base station according to the present invention issummarized as follows. Abase station (for example, a pico base stationPeNB #1) in a mobile communication system that supports a carrieraggregation technology defined in a 3GPP standard, receives informationfrom another base station (for example, a macro base station MeNB) on anX2 interface or an S1 interface, the information being used when thebase station determines a component carrier requested to be limitedlyused by the other base station or a component carrier requested to bereleased from use limitation by the other base station.

The feature of a control method according to the present invention issummarized as follows. A method of controlling a base station in amobile communication system that supports a carrier aggregationtechnology defined in a 3GPP standard, includes: a step of transmittinginformation to another base station on an X2 interface or an S1interface, the information being used when the other base stationdetermines a component carrier requested to be limitedly used by thebase station or a component carrier requested to be released from uselimitation by the base station.

The feature of a control method according to the present invention issummarized as follows. A method of controlling a base station in amobile communication system that supports a carrier aggregationtechnology defined in a 3GPP standard, includes: a step of receivinginformation from another base station on an X2 interface or an S1interface, the information being used when the base station determines acomponent carrier requested to be limitedly used by the other basestation or a component carrier requested to be released from uselimitation by the other base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an entire configuration of a mobilecommunication system according to the embodiment of the presentinvention.

FIG. 2 is a diagram for explaining the configuration of a componentcarrier that is used in the mobile communication system according to theembodiment of the present invention.

FIG. 3 is a block configuration diagram of the macro base stationaccording to the embodiment of the present invention.

FIG. 4 is a block configuration diagram of the pico base stationaccording to the embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation overview of the mobilecommunication system according to the embodiment of the presentinvention.

FIG. 6( a) is a diagram for explaining a case in which the macro basestation suspends using some of the component carriers CC #1 to CC #4.FIG. 6( b) is a diagram for explaining the case in which the macro basestation reduces the transmission power of some of the component carriersto be smaller than predetermined power.

FIG. 7 is an operation sequence diagram of the mobile communicationsystem related to the suspension of use of the component carriersaccording to the embodiment of the present invention.

FIG. 8 is an operation sequence diagram of the mobile communicationsystem related to the resumption of use of the component carrieraccording to the embodiment of the present invention.

FIG. 9 is a sequence diagram when a positive response is given to atransmission request of the information for determination according tothe embodiment of the present invention.

FIG. 10 is a sequence diagram when a negative response is given to thetransmission request of the information for determination according tothe embodiment of the present invention.

FIG. 11 is a sequence diagram at the time of transmission of theinformation for determination according to the embodiment of the presentinvention.

FIG. 12 is a sequence diagram when a positive response is given to theuse suspension request of a component carrier according to theembodiment of the present invention.

FIG. 13 is a sequence diagram when a negative response is given to theuse suspension request of a component carrier according to theembodiment of the present invention.

FIG. 14 is a sequence diagram when a positive response is given to thenotification of the use suspension/resumption of a component carrieraccording to the embodiment of the present invention.

FIG. 15 is a sequence diagram when a negative response is given to thenotification of the use suspension/resumption of a component carrieraccording to the embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENT

With reference to the drawings, the embodiment of the present inventionwill be described in the order of (1) Configuration of mobilecommunication system, (2) Operation of mobile communication system, (3)Effect of embodiment and (4) Other embodiments. In the drawings of thefollowing embodiment, the same or similar reference signs are applied tothe same or similar portions.

(1) Configuration of Mobile Communication System

(1.1) Entire Configuration

FIG. 1 is a diagram showing an entire configuration of a mobilecommunication system 1 according to the present embodiment. The mobilecommunication system 1 according to the present embodiment is configuredon the basis of LTE Advanced (after 3GPP Release 10).

As illustrated in FIG. 1, the mobile communication system 1 includesE-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 10 that is aradio access network. The E-UTRAN 10 is configured as a heterogeneousnetwork, and includes a plurality of types of base stations withdifferent transmission power (that is, service area ranges).

The heterogeneous network is for effectively arranging not only a lowpower base station (for example, a pico base station or a femto basestation) with a small service area range but also a high power basestation (that is, a macro base station). Note that the heterogeneousnetwork is capable of dispersing a load of the high power base stationto the low power base station; however, there is a problem that the lowpower base station is influenced by interference from the high powerbase station, resulting in deterioration of communication quality due tosuch inter-base station interference.

In the present embodiment, the E-UTRAN 10 includes a macro base stationMeNB that forms a large cell (a macro cell) and two pico base stationsPeNB (PeNB #1 and PeNB #2) that form small cells (pico cells).

The pico base stations PeNB #1 and PeNB #2, for example, are within theservice area of the macro base station MeNB, and are arranged in a hightraffic zone (that is, a hot zone). Note that the number of the picobase stations PeNB arranged within the service area of the macro basestation MeNB is not limited to two, and may be one or three or more.

The service area range of the macro base station MeNB is covered by aplurality of cells formed by the macro base station MeNB. Similarly, aservice area range of the pico base station PeNB #1 is covered by aplurality of cells formed by the pico base station PeNB #1, and aservice area range of the pico base station PeNB #2 is covered by aplurality of cells formed by the pico base station PeNB #2. Furthermore,the cell is a minimum unit of a radio communication area.

Each of the macro base station MeNB, the pico base station PeNB #1, andthe pico base station PeNB #2 supports the aforementioned carrieraggregation technology. In the present embodiment, one cell correspondsto one component carrier.

One or a plurality of radio terminals UE are connected to each of themacro base station MeNB, the pico base station PeNB #1, and the picobase station PeNB #2. The radio terminal UE supporting the carrieraggregation technology is capable of collectively using a plurality ofcomponent carriers for the purpose of radio communication. In otherwords, the radio terminal UE supporting the carrier aggregationtechnology is capable of simultaneously performing radio communicationwith a plurality of serving cells.

In the mobile communication system 1, an X2 interface for connecting(mutually adjacent) base stations to each other is set. In the presentembodiment, the X2 interfaces are set between the macro base stationMeNB and the pico base station PeNB #1, between the macro base stationMeNB and the pico base station PeNB #2, and between the pico basestation PeNB #1 and the pico base station PeNB #2, respectively.

Moreover, the mobile communication system 1 includes a mobilitymanagement device MME/a gateway device S-GW and an operationadministration and maintenance device OAM. The mobility managementdevice MME is configured to perform various types of mobility controlfor the radio terminal UE. The gateway device S-GW is configured toperform transfer control of user data transmitted from and received bythe radio terminal UE. The operation administration and maintenancedevice OAM is configured to perform maintenance and monitoring of theE-UTRAN 10. Between each base station eNB and EPC (the mobilitymanagement device MME/the gateway device S-GW), an S1 interface forconnecting each base station eNB to the EPC is set.

(1.2) Configuration of Component Carrier

Next, the configuration of a component carrier that is used in themobile communication system 1 will be described.

FIG. 2 is a diagram for explaining the configuration of a componentcarrier that is used in the mobile communication system 1. Hereinafter,the case, in which the number of component carriers is four, will bedescribed. However, the number of the component carriers may be two orthree, or five or more. Furthermore, the case, in which a plurality ofcomponent carriers are continuous in a frequency direction, will bedescribed. However, each of the component carriers may be dispersed inthe frequency direction. For example, the component carriers may bedispersed in an 800 MHz band and a 1.5 GHz band.

As illustrated in FIG. 2, each of the macro base station MeNB, the picobase station PeNB #1, and the pico base station PeNB #2 is capable ofusing four component carriers CC #1 to CC #4. Each of the componentcarriers CC #1 to CC #4 corresponds to a carrier (a frequency band) ofLTE. That is, each of the component carriers CC #1 to CC #4 includes aplurality of resource blocks (RB) in the frequency direction.Furthermore, the resource block is a unit of a radio resource that isassigned to the radio terminal UE.

For the purpose of convenience, power of each component carrierillustrated in FIG. 2 indicates base station transmission power of eachcomponent carrier when downlink carrier aggregation is configured. Asillustrated in FIG. 2, the transmission power of each component carrierof each of the pico base stations PeNB #1 and PeNB #2 is lower than thetransmission power of each component carrier of the macro base stationMeNB.

For this reason, each radio terminal UE connected to each of the picobase stations PeNB #1 and PeNB #2 is influenced by interference from themacro base station MeNB in each component carrier. Furthermore, since aradio terminal UE generally connects to (or waits for) a base stationfor which reception power in the radio terminal UE is the highest, aradio terminal UE located in the vicinity of the pico base station PeNB#1 or the pico base station PeNB #2 may also connect to the macro basestation MeNB.

In the present embodiment, in order to solve such a problem, the macrobase station MeNB, the pico base station PeNB #1, and the pico basestation PeNB #2 perform inter-base station interference control in unitsof component carriers in cooperation with one another. Details of suchinter-base station interference control will be described later.

(1.3) Configuration of Macro Base Station

Next, the configuration of the macro base station MeNB will bedescribed. FIG. 3 is a block configuration diagram of the macro basestation MeNB.

As illustrated in FIG. 3, the macro base station MeNB includes anantenna 101, a radio communication unit 110, a network communicationunit 120, a storage unit 130, and a control unit 140.

The antenna 101 is configured using one or a plurality of antennaelements, and is used for transmitting and receiving a radio signal.

The radio communication unit 110 is configured to perform radiocommunication by simultaneously using a plurality of component carriers.Specifically, the radio communication unit 110, for example, isconfigured using a radio frequency (RF) circuit, a baseband (BB) circuitand the like, and transmits and receives a radio signal via the antenna101 in each component carrier.

For transmission, the radio communication unit 110 performs coding andmodulation of a transmitted signal, which is input from the control unit140, performs up-conversion and amplification thereof, and then outputsthe transmitted signal to the antenna 101 in each component carrier. Forreception, the radio communication unit 110 performs amplification anddown-conversion of a received signal, which is input from the antenna101, performs demodulation and decoding thereof, and outputs thereceived signal to the control unit 140 in each component carrier.

The network communication unit 120 performs inter-base stationcommunication with a neighboring base station (the pico base stationsPeNB #1 and PeNB #2 in the present embodiment) via the X2 interface.Furthermore, the network communication unit 120 performs communicationwith a core network (that is, the mobility management device MME, thegateway device S-GW, and the operation administration and maintenancedevice OAM) via the S1 interface.

The storage unit 130 is configured using, for example, a memory, andstores various types of information that is used for control and thelike of the macro base station MeNB. In the present embodiment, thestorage unit 130 stores identification information (a cell ID) of eachcell formed by the pico base station PeNB #1 and identificationinformation (a base station ID) of the pico base station PeNB #1 to beassociated with each other. Furthermore, the storage unit 130 storesidentification information (a cell ID) of each cell formed by the picobase station PeNB #2 and identification information (a base station ID)of the pico base station PeNB #2 to be associated with each other. Asdescribed above, since component carriers differ in each cell, it ispossible to identify the component carriers by the cell ID.

The control unit 140 is configured using, for example, a CPU, andcontrols various functions provided in the macro base station MeNB. Inthe present embodiment, the control unit 140 is configured to performinter-base station interference control in units of component carriersin cooperation with the pico base stations PeNB #1 and PeNB #2.

(1.4) Configuration of Pico Base Station

Next, the configuration of the pico base station PeNB #1 will bedescribed. FIG. 4 is a block configuration diagram of the pico basestation PeNB #1. Since the pico base station PeNB #2 has the sameconfiguration as that of the pico base station PeNB #1, a descriptionfor the configuration of the pico base station PeNB #2 will be omitted.

As illustrated in FIG. 4, the pico base station PeNB #1 includes anantenna 201, a radio communication unit 210, a network communicationunit 220, a storage unit 230, and a control unit 240.

The antenna 201 is configured using one or a plurality of antennaelements, and is used for transmitting and receiving a radio signal.

The radio communication unit 210 is configured to perform radiocommunication by simultaneously using a plurality of component carriers.Specifically, the radio communication unit 210 is configured using, forexample, a radio frequency (RF) circuit, a baseband (BB) circuit and thelike, and transmits and receives a radio signal via the antenna 201 ineach component carrier.

For transmission, the radio communication unit 210 performs coding andmodulation of a transmitted signal, which is input from the control unit240, performs up-conversion and amplification thereof, and then outputsthe transmitted signal to the antenna 201 in each component carrier. Forreception, the radio communication unit 210 performs amplification anddown-conversion of a reception signal, which is input from the antenna201, performs demodulation and decoding thereof, and outputs thereception signal to the control unit 240 in each component carrier.

The network communication unit 220 performs inter-base stationcommunication with a neighboring base station (the macro base stationMeNB and the pico base station PeNB #2 in the present embodiment) viathe X2 interface. Furthermore, the network communication unit 220performs communication with a core network (that is, the mobilitymanagement device MME, the gateway device S-GW, and the operationadministration and maintenance device OAM) via the S1 interface.

The storage unit 230 is configured using, for example, a memory, andstores various types of information that is used for control and thelike of the pico base station PeNB #1. In the present embodiment, thestorage unit 230 stores identification information (a cell ID) of eachcell formed by the macro base station MeNB and identificationinformation (a base station ID) of the macro base station MeNB to beassociated with each other. As described above, since component carriersdiffer in each cell, it is possible to identify the component carriersby the cell ID.

The control unit 240 is configured using, for example, a CPU, andcontrols various functions provided in the pico base station PeNB #1. Inthe present embodiment, the control unit 240 is configured to performinter-base station interference control in units of component carriersin cooperation with the macro base station MeNB.

(2) Operation of Mobile Communication System

(2.1) Operation Overview

Next, with reference to FIG. 5 and FIG. 6, the operation overview of themobile communication system 1 will be described. FIG. 5 is a diagram forexplaining the operation overview of the mobile communication system 1.

As illustrated in FIG. 5, the pico base stations PeNB #1 and PeNB #2 arearranged within the service area of the macro base station MeNB.Furthermore, among a plurality of radio terminals UE located within theservice area of the macro base station MeNB, a radio terminal UE #1 isconnected to the pico base station PeNB #1, a radio terminal UE #2 isconnected to the pico base station PeNB #2, and other radio terminals UEare connected to the macro base station MeNB.

As described above, each radio terminal UE connected to each of the picobase stations PeNB #1 and PeNB #2 is influenced by interference from themacro base station MeNB in each component carrier, resulting in thedeterioration of communication quality. Furthermore, since a radioterminal UE #3 located in the vicinity of the pico base station PeNB #1and a radio terminal UE #4 located in the vicinity of the pico basestation PeNB #2 are connected to the macro base station MeNB, it is notpossible to disperse a load of the macro base station MeNB.

For this reason, the macro base station MeNB suspends using some of thecomponent carriers CC #1 to CC #4 or reduces the transmission power ofthe some component carriers according to the situation within theservice area of the macro base station MeNB.

FIG. 6( a) is a diagram for explaining a case in which the macro basestation MeNB suspends using some of the component carriers CC #1 to CC#4. As illustrated in FIG. 6( a), the macro base station MeNB suspendsusing the component carriers CC #3 and CC #4, so that each of the picobase stations PeNB #1 and PeNB #2 avoids the influence of interferencefrom the macro base station MeNB in the component carriers CC #3 and CC#4.

FIG. 6( b) is a diagram for explaining the case in which the macro basestation MeNB reduces the transmission power of some of the componentcarriers CC #1 to CC #4 to be smaller than predetermined power. Asillustrated in FIG. 6( b), when the macro base station MeNB reduces thetransmission power of the component carriers CC #3 and CC #4 to besmaller than the predetermined power, the influence of interference ineach of the pico base stations PeNB #1 and PeNB #2 from the macro basestation MeNB in the component carriers CC #3 and CC #4 is reduced.

As a consequence, it is possible to improve the communication quality ofthe radio terminal UE #1 connected to the pico base station PeNB #1 andthe communication quality of the radio terminal UE #2 connected to thepico base station PeNB #2, and it is possible to increase theprobability that the radio terminal UE #3 located in the vicinity of thepico base station PeNB #1 connects to the pico base station PeNB #1 andthe probability that the radio terminal UE #4 located in the vicinity ofthe pico base station PeNB #2 connects to the pico base station PeNB #2.

The macro base station MeNB and the pico base stations PeNB (PeNB #1 andPeNB #2) exchange information related to such component carrier control,so that it is possible to avoid a problem due to the suspension of use(or the transmission power reduction) of component carriers by the macrobase station MeNB, and to increase the improvement effect obtained bythe suspension of use (or the transmission power reduction) of thecomponent carriers.

(2.2) Operation Sequence

Hereinafter, the operation sequence of the mobile communication system 1will be described while focusing on inter-base station signaling betweenthe macro base station MeNB and the pico base stations PeNB (PeNB #1 andPeNB #2).

Firstly, the operation sequence of the mobile communication system 1related to the suspension of use of component carriers will bedescribed. FIG. 7 is an operation sequence diagram of the mobilecommunication system 1 related to the suspension of use of the componentcarriers.

As illustrated in FIG. 7, in step S11, the pico base station PeNB #1transmits information to the macro base station MeNB via the X2interface, wherein the information is used for determining a componentcarrier that is subject to suspension of use by the macro base stationMeNB. The macro base station MeNB receives the information.

Furthermore, as the information for determining the component carriersubject to suspension of use by the macro base station MeNB, forexample, it is possible to use at least one item of the following firstinformation to fifth information.

The first information is information indicating a component carrieravailable by a radio terminal UE supporting no carrier aggregationtechnology from among each of the radio terminals UE located within theservice area of the pico base station PeNB #1 (or connected to the picobase station PeNB #1), or a component carrier not available by the radioterminal UE supporting no carrier aggregation technology. For example,if the macro base station MeNB suspends using the component carrieravailable by the radio terminal UE, since there is a problem that theradio terminal UE is not able to perform handover (or cell reselection)to the macro base station MeNB from the pico base station PeNB #1, it iseffective to notify the macro base station MeNB of the information inorder to prevent the problem.

The second information is information indicating a band available by aradio terminal UE having a limited available band (frequency band) fromamong each of the radio terminals UE located within the service area ofthe pico base station PeNB #1 (or connected to the pico base stationPeNB #1), or a band not available by the radio terminal UE having alimited available band. For example, a case is assumed in which a radioterminal UE capable of using only an 800 MHz band is located within theservice area of the pico base station PeNB #1. If the macro base stationMeNB suspends using all component carriers corresponding to the 800 MHzband, since there is a problem that the radio terminal UE is not able toperform handover (or cell reselection) to the macro base station MeNBfrom the pico base station PeNB #1, it is effective to notify the macrobase station MeNB of the information in order to prevent the problem.

Note that the pico base station PeNB #1 is capable of acquiring theaforementioned first information and second information on the basis ofcommunication capability information (UE Capability) that is notified tothe pico base station PeNB #1 by the radio terminal UE connected to thepico base station PeNB #1. Alternatively, the pico base station PeNB #1may acquire the aforementioned first information and second informationby performing inquiry for the mobility management device MME or theoperation administration and maintenance device OAM.

The third information is information indicating the communicationcapability of the pico base station PeNB #1. For example, a case isassumed in which component carriers available by the pico base stationPeNB #1 are limited to the component carriers CC #1 and CC #2 due to thecapability of the pico base station PeNB #1. When the macro base stationMeNB is capable of using the component carriers CC #1 to CC #4, since itis preferable that the macro base station MeNB suspends using thecomponent carrier CC #1 and/or CC #2, it is effective to notify themacro base station MeNB of the information.

The fourth information is information indicating a downlink interferencelevel of each component carrier, which is received in the pico basestation PeNB #1 from the macro base station MeNB. For example, since itis preferable that the macro base station MeNB suspends using acomponent carrier that gives large interference to the pico base stationPeNB #1 in a downlink, it is effective to notify the macro base stationMeNB of the information. Note that the pico base station PeNB #1 iscapable of acquiring the aforementioned first information and secondinformation on the basis of radio state information (CQI and the like)that is notified to the pico base station PeNB #1 from the radioterminal UE connected to the pico base station PeNB #1.

In step S12, the pico base station PeNB #2 transmits the information tothe macro base station MeNB via the X2 interface, wherein theinformation is used for determining the component carrier capable ofbeing subject to suspension of use by the macro base station MeNB. Themacro base station MeNB receives the information. Furthermore, as theinformation for determining the component carrier subject to suspensionof use by the macro base station MeNB, it is possible to use at leastone item of the aforementioned first information to fifth information.

In step S13, the macro base station MeNB performs determinationregarding the component carrier capable of being subject to suspensionof use. Specifically, the macro base station MeNB determines whether themacro base station MeNB can suspend some component carrier anddetermines which component carrier is effective to be suspended. On thebasis of the aforementioned first information to fifth information, themacro base station MeNB performs determination regarding the componentcarrier capable of being subject to suspension of use such that aproblem due to the suspension of use of the component carrier is avoidedand an improvement effect obtained by each of the pico base stationsPeNB #1 and PeNB #2 is increased.

In step S14, the macro base station MeNB notifies (broadcasts) the picobase stations PeNB #1 and PeNB #2 of the component carrier capable ofbeing subject to suspension of use, via the X2 interface. The pico basestations PeNB #1 and PeNB #2 receive the notification. In the presentembodiment, the notification of the component carrier capable of beingsubject to suspension of use, is performed by notifying a cell ID of acell corresponding to the component carrier capable of being subject tosuspension of use.

Note that, in the step S14, instead of notifying (broadcasting) thecomponent carrier capable of being subject to suspension of use, acomponent carrier not capable of being subject to suspension of use, maybe notified (broadcasted). Even through the notification (broadcast),the pico base stations PeNB #1 and PeNB #2 are able to recognize thecomponent carrier capable of being subject to suspension of use.

In step S15#1, the pico base station PeNB #1 performs determinationregarding a component carrier for which suspension of use should berequested, on the basis of the notification of the component carriercapable of being subject to suspension of use, from the macro basestation MeNB and a situation (for example, the aforementioned firstinformation to fifth information) within the service area of the picobase station PeNB #1. In the present embodiment, the pico base stationPeNB #1 determines whether to request the suspension of use of thecomponent carrier capable of being subject to suspension of use. Thepico base station PeNB #1 performs determination such that a problem dueto the suspension of use of the component carrier is avoided and animprovement effect obtained by the pico base station PeNB #1 isincreased. Furthermore, it is assumed that the pico base station PeNB #1has determined to request the suspension of use of the component carriercapable of being subject to suspension of use.

In step S15#2, the pico base station PeNB #2 performs determinationregarding a component carrier for which suspension of use should berequested, on the basis of the notification of the component carriercapable of being subject to suspension of use, from the macro basestation MeNB and a situation (for example, the aforementioned firstinformation to fifth information) within the service area of the picobase station PeNB #2. In the present embodiment, the pico base stationPeNB #2 determines whether to request the suspension of use of thecomponent carrier capable of being subject to suspension of use. Thepico base station PeNB #2 performs determination such that a problem dueto the suspension of use of the component carrier is avoided and animprovement effect obtained by the pico base station PeNB #2 isincreased. Furthermore, it is assumed that the pico base station PeNB #2has determined not to request the suspension of use of the componentcarrier capable of being subject to suspension of use.

In step S16, the pico base station PeNB #1 requests the macro basestation MeNB to suspend using the component carrier capable of beingsubject to suspension of use, via the X2 interface. In the presentembodiment, the use suspension request of a component carrier isperformed by notifying a cell ID of a cell corresponding to a componentcarrier the suspension of use of which is requested. On the basis of theuse suspension request received from the pico base station PeNB #1, itis assumed that the macro base station MeNB has determined to suspendusing the component carrier the suspension of use of which is requested.

In step S17, the macro base station MeNB notifies (broadcasts) the picobase stations PeNB #1 and PeNB #2 of the component carrier subject tosuspension of use via the X2 interface. The pico base stations PeNB #1and PeNB #2 receive the notification. In the present embodiment, thenotification of the component carrier subject to suspension of use isperformed by notifying a cell ID of a cell corresponding to thecomponent carrier subject to suspension of use. The notification mayinclude information (for example, information on how many subframes mustpass to suspend the component carrier) indicating a timing at which thesuspension of use is executed.

In step S18, the macro base station MeNB performs the suspension of useof the component carrier when a predetermined time lapsed from thenotification of the suspension of use (step S17). For example, the macrobase station MeNB allows the transmission power of the component carrierto be suspended to be zero. Alternatively, instead of using an elapse ofa predetermined time as a suspension condition, it may be possible toemploy a suspension condition that a positive response for thenotification of the suspension of use has been obtained from each of thepico base stations PeNB #1 and PeNB #2.

The pico base station PeNB (PeNB #1 or PeNB #2) received thenotification (step S17) of the suspension of use of the componentcarrier, for example, may perform at least one of the following firstoperation or second operation.

According to the first operation, the pico base station PeNBpreferentially assigns a resource block, which is included in thecomponent carrier for which the suspension of use has been notified, toa radio terminal UE that supports the carrier aggregation technologyamong radio terminals UE connected to the pico base station PeNB.

According to the second operation, the pico base station PeNBpreferentially performs handover to a cell, which corresponds to thecomponent carrier for which the suspension of use has been notified, toa radio terminal UE that supports no carrier aggregation technologyamong the radio terminals UE connected to the pico base station PeNB.

Note that in the present operation sequence, the suspension of use ofthe component carrier is performed (step S18) after the suspension ofuse of the component carrier is notified (step S17). However, thesuspension of use of the component carrier may be performed before thesuspension of use of the component carrier is notified or simultaneouslyto the notification.

Next, an operation sequence of the mobile communication system 1 relatedto the resumption of use of a component carrier will be described. FIG.8 is an operation sequence diagram of the mobile communication system 1related to the resumption of use of the component carrier.

As illustrated in FIG. 8, in step S21, the pico base station PeNB #1transmits information to the macro base station MeNB via the X2interface, wherein the information is used for determining a componentcarrier subject to resumption of use by the macro base station MeNB. Themacro base station MeNB receives the information. Furthermore, as theinformation for determining the component carrier subject to resumptionof use by the macro base station MeNB, for example, it is possible touse at least one item of the aforementioned first information to fifthinformation.

In step S22, the pico base station PeNB #2 transmits the information tothe macro base station MeNB via the X2 interface, wherein theinformation is used for determining the component carrier capable ofbeing subject to resumption of use by the macro base station MeNB. Themacro base station MeNB receives the information. Furthermore, as theinformation for determining the component carrier subject to resumptionof use by the macro base station MeNB, it is possible to use at leastone item of the aforementioned first information to fifth information.

In step S23, the macro base station MeNB performs determinationregarding the component carrier capable of being subject to resumptionof use. Specifically, the macro base station MeNB determines whether themacro base station MeNB can resume using some component carrier anddetermines which component carrier is to be resumed to be used in orderto obtain effectiveness. On the basis of the aforementioned firstinformation to fifth information, the macro base station MeNB performsdetermination regarding the component carrier subject to resumption ofuse such that a problem due to the resumption of use of the componentcarrier is avoided.

In step S24, the macro base station MeNB notifies (broadcasts) the picobase stations PeNB #1 and PeNB #2 of the component carrier subject toresumption of use via the X2 interface. The pico base stations PeNB #1and PeNB #2 receive the notification. In the present embodiment, thenotification of the component carrier capable of being subject toresumption of use is performed by notifying a cell ID of a cellcorresponding to the component carrier subject to resumption of use.

Note that, in the step S24, instead of notifying (broadcasting) thecomponent carrier capable of being subject to resumption of use, acomponent carrier not capable of being subject to resumption of use, maybe notified (broadcasted). Even through the notification (broadcast),the pico base stations PeNB #1 and PeNB #2 are able to recognize thecomponent carrier capable of being subject to resumption of use.

In step S25#1, the pico base station PeNB #1 performs determinationregarding a component carrier for which resumption of use should berequested, on the basis of the notification of the component carriercapable of being subject to resumption of use, from the macro basestation MeNB and a situation (for example, the aforementioned firstinformation to fifth information) within the service area of the picobase station PeNB #1. In the present embodiment, the pico base stationPeNB #1 determines whether to request the resumption of use of thecomponent carrier capable of being subject to resumption of use. Thepico base station PeNB #1 performs determination such that a problem dueto the resumption of use of the component carrier is avoided.Furthermore, it is assumed that the pico base station PeNB #1 hasdetermined to request the resumption of use of the component carriercapable of being subject to resumption of use.

In step S25#2, the pico base station PeNB #2 performs determinationregarding a component carrier for which resumption of use should berequested, on the basis of the notification of the component carriercapable of being subject to resumption of use, from the macro basestation MeNB and a situation (for example, the aforementioned firstinformation to fifth information) within the service area of the picobase station PeNB #2. In the present embodiment, the pico base stationPeNB #2 determines whether to request the resumption of use of thecomponent carrier capable of being subject to resumption of use. Thepico base station PeNB #2 performs determination such that a problem dueto the resumption of use of the component carrier is avoided.Furthermore, it is assumed that the pico base station PeNB #2 hasdetermined not to request the resumption of use of the component carriercapable of being subject to resumption of use.

In step S26, the pico base station PeNB #1 requests the macro basestation MeNB to resume using the component carrier capable of beingsubject to resumption of use, via the X2 interface. In the presentembodiment, the use resumption request of a component carrier isperformed by notifying a cell ID of a cell corresponding to a componentcarrier the resumption of use of which is requested. On the basis of theuse resumption request received from the pico base station PeNB #1, itis assumed that the macro base station MeNB has determined to resumeusing the component carrier for which resumption of use should berequested.

In step S27, the macro base station MeNB notifies (broadcasts) the picobase stations PeNB #1 and PeNB #2 of a component carrier subject toresumption of use via the X2 interface. The pico base stations PeNB #1and PeNB #2 receive the notification. In the present embodiment, thenotification of the component carrier subject to resumption of use isperformed by notifying a cell ID of a cell corresponding to thecomponent carrier subject to resumption of use. The notification mayinclude information (for example, information on how many subframes mustpass to resume using the component carrier) indicating a timing at whichthe resumption of use is performed.

In step S28, the macro base station MeNB performs the resumption of useof the component carrier when a predetermined time has lapsed after thenotification (step S27) of the resumption of use. For example, the macrobase station MeNB returns the transmission power of the componentcarrier subject to resumption to an original level (a standard level).Alternatively, instead of the resumption condition that thepredetermined time lapses, it may be possible to employ a resumptioncondition that a positive response for the notification of theresumption of use is obtained from each of the pico base stations PeNB#1 and PeNB #2.

The pico base station PeNB (PeNB #1 or PeNB #2) which receives thenotification (step S27) of the resumption of use of the componentcarrier may return to a normal state, or for example, may perform atleast one of the following first operation and second operation.

According to the first operation, the pico base station PeNB does notassign a resource block, if possible, which is included in the componentcarrier for which the resumption of use has been notified, to a radioterminal UE that supports the carrier aggregation technology among radioterminals UE connected to the pico base station PeNB.

According to the second operation, the pico base station PeNBpreferentially performs handover to another cell from a cell, whichcorresponds to the component carrier for which the resumption of use hasbeen notified, with respect to a radio terminal UE that supports nocarrier aggregation technology among the radio terminals UE connected tothe pico base station PeNB.

Note that in the present operation sequence, the resumption of use ofthe component carrier is performed (step S28) after the resumption ofuse of the component carrier is notified (step S27), however, theresumption of use of the component carrier may be performed before or atthe timing of the notification of the resumption of use of the componentcarrier.

In the aforementioned operation sequence, the macro base station MeNBsuspends or resumes the use of a component carrier. However, the“suspension of use” of FIG. 7 is replaced with “transmission powerreduction” and the “resumption of use” of FIG. 8 is replaced with“transmission power increase (or transmission power returning)”, so thatit is possible to apply the aforementioned operation sequence to thetransmission power reduction/increase of the component carrier.

Furthermore, in the aforementioned operation sequence, a parameter fordetermining the use suspension/resumption of a component carrier may beprovided by the operation administration and maintenance device OAM. Forexample, when the macro base station MeNB determines not to perform theuse suspension/the use resumption until the number of received usesuspension requests/use resumption requests exceeds a threshold value,the operation administration and maintenance device OAM may set thethreshold value in the macro base station MeNB.

Moreover, the present embodiment described the operation sequence inwhich the use resumption request of a component carrier is transmittedfrom the pico base station PeNB #1 to the macro base station MeNB.However, instead of such an operation sequence, it may be determined toresume the use of a component carrier when the macro base station MeNBdoes not receive the use suspension request of the component carrier fora predetermined time.

(2.3) Detailed Example of Inter-Base Station Signaling

Hereinafter, a description will be provided for a detailed example ofinter-base station signaling that is used in the aforementionedoperation sequence.

Firstly, with reference to FIG. 9 to FIG. 11, a description will beprovided for a detailed example of inter-base station signaling relatedto the transmission and reception of information (hereinafter,“information for determination”) for determining a component subject tosuspension of use or a component carrier subject to resumption of use.In FIG. 9 to FIG. 11, eNB 1 corresponds to, for example, the macro basestation MeNB and eNB 2 corresponds to, for example, the pico basestation PeNB #1 or PeNB #2.

FIG. 9 is a sequence diagram when a positive response is given to atransmission request of the information for determination.

As illustrated in FIG. 9, the eNB 1 transmits CC Status Request, whichis a message for requesting a periodic report of the information fordetermination, to the eNB 2 via the X2 interface. The CC Status Requestmay include a cell ID for designating a cell, ID of informationrequested to be reported among the aforementioned first information tofifth information, and information on a time interval at which a reportis performed. After the CC Status Request is received, the eNB 2transmits CC Status Response, which is a positive response message forthe CC Status Request, to the eNB 1 via the X2 interface. Note that theCC Status Response may also include at least one item of theaforementioned first information to fourth information.

FIG. 10 is a sequence diagram when a negative response is given to thetransmission request of the information for determination.

As illustrated in FIG. 10, the eNB 1 transmits CC Status Request, whichis a message for requesting a periodic report of the information fordetermination, to the eNB 2 via the X2 interface. The CC Status Requestmay include a cell ID for designating a cell, and ID of informationrequested to be reported among the aforementioned first information tofifth information. After the CC Status Request is received, the eNB 2transmits CC Status Failure, which is a negative response message forthe CC Status Request, to the eNB 1 via the X2 interface. Note that theCC Status Failure may also include at least one of the aforementionedfirst information to fourth information.

FIG. 11 is a sequence diagram at the time of transmission of theinformation for determination. The operation sequence of FIG. 11 isperformed after the eNB 2 transmits the CC Status Response. However, theoperation sequence is not performed after the eNB 2 transmits the CCStatus Failure.

As illustrated in FIG. 11, the eNB 2 transmits CC Status Update, whichis a message including the information for determination (theinformation requested to be reported among the aforementioned firstinformation to fifth information) to the eNB 1 via the X2 interface.Note that a periodic report of the CC Status Update may be continueduntil the eNB 1 requests the eNB 2 to suspend the periodic report.

Note that the aforementioned sequences of FIG. 9 and FIG. 10 may beomitted, and predetermined type of information may be transmitted fromthe eNB 2 to the eNB 1.

Next, with reference to FIG. 12 and FIG. 13, a description will beprovided for a detailed example of inter-base station signaling relatedto the use suspension request. In FIG. 12 and FIG. 13, eNB 1, forexample, corresponds to the pico base station PeNB #1 or PeNB #2 and eNB2, for example, corresponds to the macro base station MeNB.

FIG. 12 is a sequence diagram when a positive response is given to theuse suspension request of a component carrier.

As illustrated in FIG. 12, the eNB 1 transmits Cell Muting Request,which is a message for requesting the suspension of use of a componentcarrier, to the eNB 2 via the X2 interface. The Cell Muting Requestincludes a cell ID of a cell corresponding to a component carrier thesuspension of use of which is requested. After the Cell Muting Requestis received, the eNB 2 transmits Cell Muting Response, which is apositive response message for the Cell Muting Request, to the eNB 1 viathe X2 interface.

Note that, instead of the message for requesting the suspension of useof a component carrier, in the case of using the message for requestingtransmission power reduction of the component carrier, a parameter(direct designation or two values of small and large values) fordesignating a requested transmission power reduction amount (dB by whichtransmission power is reduced) may be controlled to be included into amessage for requesting transmission power reduction and may betransmitted.

FIG. 13 is a sequence diagram when a negative response is given to theuse suspension request of a component carrier.

As illustrated in FIG. 13, the eNB 1 transmits Cell Muting Request,which is a message for requesting the suspension of use of a componentcarrier, to the eNB 2 via the X2 interface. The Cell Muting Requestincludes a cell ID of a cell corresponding to a component carrier thesuspension of use of which is requested. After the Cell Muting Requestis received, the eNB 2 transmits Cell Muting Failure, which is anegative response message for the Cell Muting Request, to the eNB 1 viathe X2 interface.

Note that, as the use resumption request of a component carrier, CellActivation Request is available. The Cell Activation Request includes acell ID of a cell corresponding to a component carrier the resumption ofuse of which is requested.

Next, with reference to FIG. 14 and FIG. 15, a description will beprovided for a detailed example of inter-base station signaling relatedto the notification of a component carrier subject to suspension of useor the notification of a component carrier subject to resumption of use.In FIG. 14 and FIG. 15, eNB 1 corresponds to, for example, the macrobase station MeNB and eNB 2 corresponds to, for example, the pico basestation PeNB #1 or PeNB #2.

FIG. 14 is a sequence diagram when a positive response is given to thenotification of the use suspension/resumption of a component carrier.

As illustrated in FIG. 14, the eNB 1 transmits eNB Configuration Update,which is a message including information indicating the usesuspension/resumption of a component carrier, to the eNB 2 via the X2interface. The information indicating the suspension of use of acomponent carrier is, for example, Cell Deactivation Indication IE. TheCell Deactivation Indication IE includes a cell ID corresponding to acomponent carrier subject to suspension of use. Furthermore, theinformation indicating the resumption of use of a component carrier is,for example, Cell Activation Indication IE. The Cell ActivationIndication IE includes a cell ID corresponding to a component carriersubject to resumption of use. After the eNB Configuration Update isreceived, the eNB 2 transmits eNB Configuration Update Acknowledge,which is a positive response message for the eNB Configuration Update,to the eNB 1 via the X2 interface.

FIG. 15 is a sequence diagram when a negative response is given to thenotification of the use suspension/resumption of a component carrier.

As illustrated in FIG. 15, the eNB 1 transmits eNB configuration Update,which is a message including information indicating the usesuspension/resumption of a component carrier, to the eNB 2 via the X2interface. The information indicating the suspension of use of acomponent carrier is, for example, Cell Deactivation Indication IE, andthe information indicating the suspension of use of a component carrieris, for example, Cell Activation Indication IE. After the eNBconfiguration Update is received, the eNB 2 transmits eNB ConfigurationUpdate Failure, which is a negative response message for the eNBConfiguration Update, to the eNB 1 via the X2 interface. When the eNBConfiguration Update Failure is received, the eNB 1 cancels the usesuspension/resumption of the component carrier.

Note that in FIG. 14 and FIG. 15, an example, in which the eNBConfiguration Update is used, was described. However, the usesuspension/resumption of a component carrier may be notified throughanother message. For example, Cell Type IE included in Last Visited CellInformation of UE History Information may be used and included into anewly defined message.

(3) Effect of Embodiment

As described above, the inter-base station signaling, in which the macrobase station MeNB and the pico base stations PeNB (PeNB #1 and PeNB #2)perform the inter-base station interference control in units ofcomponent carriers in cooperation with each other, is defined, so thatit is possible to avoid a problem due to the suspension of use (or thetransmission power reduction) of a component carrier by the macro basestation MeNB, and to increase the improvement effect obtained by thesuspension of use (or the transmission power reduction) of the componentcarrier.

Furthermore, the aforementioned operation sequence is periodicallyperformed, so that the macro base station MeNB is capable of adaptively(dynamically) performing the use suspension/resumption (or transmissionpower reduction/increase) of a component carrier. In this way, it ispossible to increase an interference reduction effect and to reduce thepower consumption of the macro base station MeNB.

(4) Other Embodiments

As described above, the present invention has been described accordingto the embodiment. However, it must not be understood that thediscussions and the drawings constituting a part of this disclosurelimit the present invention. From this disclosure, various alternativeembodiments, examples and operational techniques are apparent to thoseskilled in the art.

In the aforementioned embodiment, the macro base station MeNB and thepico base station PeNB exchange various types of information via the X2interface (on the X2 interface). However, the present invention is notlimited to the X2 interface. The macro base station MeNB and the picobase station PeNB may exchange various types of information via an S1interface (on an X1 interface). For example, it may be possible toemploy a configuration in which the aforementioned various types ofinformation (or messages) is transmitted via the mobility managementdevice MME, the operation administration and maintenance device OAM andthe like.

The aforementioned embodiment described the case in which the macro basestation MeNB performs the use suspension/resumption (or transmissionpower reduction/increase) of a component carrier. However, the pico basestation PeNB may perform the use suspension/resumption (or transmissionpower reduction/increase) of a component carrier. In this case, it issufficient if the relation between the macro base station MeNB and thepico base station PeNB in the aforementioned operation sequence isreversed.

Furthermore, the aforementioned embodiment mainly described signalingbetween different types of base stations in the heterogeneous network.However, since inter-base station interference may also occur betweenthe macro base stations or between the pico base stations, the presentinvention may also be applied to signaling between the same type of basestations.

Note that, in LTE Advanced, since it is expected that a relay node thatis a base station that configures a backhaul in radio is employed andthat the X2 interface is also employed for the relay node, the relaynode may be employed as the base station according to the presentinvention.

Furthermore, in the future, it is considered that one component carrieris divided and each divided carrier is dealt as a new component carrier.Accordingly, the term “component carrier” in the present specificationis assumed to include such a new component carrier.

Accordingly, it must be understood that the present invention includesvarious embodiments and the like that are not described herein.

The entire content of Japanese Patent Application No. 2011-098824 (filedon Apr. 26, 2011) is incorporated herein by reference.

INDUSTRIAL APPLICABILITY

As described above, since a base station and a control method thereofaccording to the present invention are able to reduce interference in acarrier aggregation technology, they are applicable to a radiocommunication field such as mobile communication.

1. A base station in a mobile communication system that supports acarrier aggregation technology defined in a 3GPP standard, transmittinginformation to another base station on an X2 interface or an S1interface, the information being used when the other base stationdetermines a component carrier requested to be limitedly used by thebase station or a component carrier requested to be released from uselimitation by the base station.
 2. A base station in a mobilecommunication system that supports a carrier aggregation technologydefined in a 3GPP standard, receiving information from another basestation on an X2 interface or an S1 interface, the information beingused when the base station determines a component carrier requested tobe limitedly used by the other base station or a component carrierrequested to be released from use limitation by the other base station.3. A method of controlling a base station in a mobile communicationsystem that supports a carrier aggregation technology defined in a 3GPPstandard, comprising: a step of transmitting information to another basestation on an X2 interface or an S1 interface, the information beingused when the other base station determines a component carrierrequested to be limitedly used by the base station or a componentcarrier requested to be released from use limitation by the basestation.
 4. A method of controlling a base station in a mobilecommunication system that supports a carrier aggregation technologydefined in a 3GPP standard, comprising: a step of receiving informationfrom another base station on an X2 interface or an S1 interface, theinformation being used when the base station determines a componentcarrier requested to be limitedly used by the other base station or acomponent carrier requested to be released from use limitation by theother base station.